The purpose of the present proposal is to study the dynamics of gas exchange at the levels of the lung, blood, and tissue. The following studies are proposed: 1) To determine the effect of varying inspired oxygen and carbon dioxide concentration on the distribution of VA/Q in normal humans; 2) To measure the Bohr factors at varying base excess and PCO2 to amplify on data previously obtained on hemoglobin-ligand interaction; 3) To measure the effect of temperature on hemoglobin- ligand interaction; 4) To study ligand interaction with maternal and fetal sheep blood to provide information for ongoing artificial placenta preparations; and 5) To develop a model of the sytemic tissue capillary and gas exchange.